A Lebanon-based Sunni armed group close to al-Qaeda has claimed responsibility.

"This is a double-martyrdom operation carried out by two heroes from the heroic Sunnis of Lebanon," Sirajeddin Zreikat, a member of the group, wrote on Twitter.

"Operations will continue in Lebanon until two demands are met: first, withdrawing Hezbollah members from Syria; second, release our prisoners from jails of injustice in Lebanon."

Fighters from the Shia group Hezbollah fought alongside Assad's forces in several strategic battles in Syria against mainly Sunni Muslim rebels. Iran has been bank-rolling Assad's fight, and also supports Hezbollah in Lebanon.

There have been several bomb attacks in Beirut and the northern city of Tripoli linked to the conflict in neighbouring Syria.